If you are an information gathering geek, and if you search specifically for WikiPedia's never ending knowledge articles, GooglePedia Extension for Firefox is the best option for you. This free add-on brings you Wikipedia articles most closely matching to your search terms in the splitted screen along with the usual Google Search Results, side by side. It gives you the comfort of expanding, shrinking the splitted screen. You can even hide the article screen if you only want to search Google.

In addition to that, clicking links in the Wikipedia articles trigger new Google searches, making it a very useful research tool. It works smoothly with Firefox 1.5-3.0. Below is a screen shot that will give you broader idea on how it looks.